This invention pertains to the art of heat exchanging devices and more particularly to heat exchanging devices comprising a plurality of assembled heat exchanger plates.
The invention is particularly applicable to a plate and frame heat exchanger assembly that employs sea water as a heat exchange fluid in the assembly. However, it will be appreciated by those skilled in the art that the invention could be readily adapted for use with other types of fluids as, for example, where similar heat exchanger assemblies are employed with plate-fouling fluids in the course of operation.
A great portion of conventional heat exchanger assemblies use sea water as a cooling fluid in the heat exchanger operation. As sea water is comprised of many elemental and organic items, such assemblies suffer the problems of deposits forming on heat exchange surfaces which affect heat transfer operation. Where the deposits are primarily organic the build-up is referred to as biofouling. Chemical deposits are generally referred to as scale. As biofouling and scale deposits build up on a heat exchanger surface, the heat exchanger operational efficiency diminishes to the point where it becomes necessary to either chemically or mechanically remove the deposits from the heat exchange surfaces. The problems of biofouling and scale deposit are so prevalent that it is a common industry practice to intentionally over-design heat exchanger capacities to allow for the diminishing efficiency resulting from such deposits.
An improved method for controlling biofouling and scale is disclosed in U.S. Pat. Nos. 4,256,556 and 4,345,981 which disclose a method of anodically polarizing surfaces to define an electrolytic chamber for sea water in order to effect biofouling and scale control. However, problems have arisen in the attempts to apply the method of these patents to conventional plate heat exchanger constructions. More particularly, most conventional plate heat exchanger assemblies include opposed heat exchange plates which are in electrically conductive contact and which, therefore, are unsuitable for anodic polarization.
In a plate heat exchanger, the plates are typically constructed of titanium and are designed to be as thin as possible in their cross-sectional dimension to maximize heat exchange efficiency. Such plates are very flexible and when assembled and compressed in a plate heat exchanger frame, are frequently deformed into abutting contact. Attempts to maintain a separation of the plates to define an electrolytic chamber by mere spacing of the plates with perimeter sealing gaskets have been largely unsuccessful due to the pliancy of the plates and, more importantly, because of the operational desirability of maintaining the plates in as close a contact as possible. Coating of an entire plate surface with an insulator material to avoid electrically conductive contact between the plates has also proved undesirable in that the coating over the plate acts itself as a surface deposit which diminishes heat exchange efficiency. Although such electrically insulated plates could likely employ the method of the aforementioned patents, the heat exchanger operation of such a construction would be unacceptable.
The present invention contemplates a new and improved device which overcomes all of the above problems and others to provide a new plate heat exchanger assembly which is simple in design, economical to manufacture, readily adaptable to a plurality of heat exchanger plate configurations having a variety of dimensional characteristics, easy to apply and which provides improved plate heat exchanger assembly operation.